This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from my application entitled LASER SCANNING UNIT filed with the Korean Industrial Property Office on 27 Mar. 2000 and there duly assigned Ser. No. 2000/15538.
1. Field of the Invention
The present invention relates to laser scanning unit, more particularly to laser scanning unit for forming an image on a photo-sensitive drum by generating laser beams in a facsimile, a copying machine and a printer using laser beams.
2. Description of the Related Art
In general, a laser printer is an apparatus reviving a picture image by forming images with laser beams emitted from a laser diode by a video signal of an input image on a photo-sensitive drum and by transcribing a latent image formed on the photo-sensitive drum on a medium such as a paper.
Like said, a laser printer includes a sheet cassette where a number of papers are received, a paper feeding part for feeding a paper by picking up the paper in the sheet cassette, a laser scanning unit for forming an image on a photo-sensitive drum by generating laser beams, a printing part forming an image on a paper fed from the paper feeding part by a potential difference between a toner and a transcribing roller imaged on the photo-sensitive drum, and a paper ejecting part.
For example, U.S. Pat. No. 6,104,519 for a Multi-Beam Exposure Unit to Shiraishi et al., discloses a schematic plan view illustrating the layout of optical members of a light scanning unit built in the image forming apparatus. Element number 25 is a horizontal synchronization detection mirror or Beam Detect or BD mirror. Light from the horizontal synchronization detection mirror 25 is sent to a horizontal synchronization detector 23 for timing of writing an image along one scanning line of an image forming apparatus. Similar apparatuses are illustrated in U.S. Pat. No. 6,081,289 for an Intensity Control Unit For Image Forming Apparatuses to Ogasawara et al., and U.S. Pat No. 5,606,449 for an Optical Scanning Device to Nishiyama. However, none of these references discuss the structure of the horizontal synchronization mirror. What is needed is a simple and effective design to reflect horizontally a beam into a detection device for synchronization purposes for an image forming apparatus.
It is therefore an object of the present invention to provide an improved device for reflecting a beam horizontally with respect to the image forming apparatus.
It is yet another object of the present invention to provide a simplified apparatus for horizontally reflecting a beam in an image forming apparatus.
It is yet another object to provide a more efficient apparatus for horizontally reflecting a beam in an image forming apparatus.
It is also an object to use a reflective film on a reflective surface instead of the horizontal synchronization mirror to reflect horizontally a beam.
According to one aspect of the present invention, a laser scanning unit of the present invention includes: a collimated lens reforming laser beams emitted from a laser diode into parallel beams; a polygon mirror scanning by deflecting the laser beams passing through said collimated lens in constant velocity; a f-theta lens adjusting a focus on a scanning plane by polarizing the laser beams reflected by said polygon mirror into a main scanning direction and correcting an aberration; a reflecting surface attached with a reflecting film reflecting the laser beams into a horizontal direction; an optical sensor receiving the laser beams reflected by the reflecting film; and a base plate for supporting the optical sensor and reflecting surface. It is desirable that the reflecting surface is made in a body with the base plate during plastic injection molding of the base plate, and the reflecting film is an aluminum thin film having good reflecting property of laser beams.
According to the present invention like the above, it is not needed to have an additional horizontal synchronous mirror and a plate spring fixing thereof as before, by reflecting laser beams by attaching a reflective film to a reflecting surface formed by being projected on a base plate in a body, instead of a horizontal synchronous mirror fixed by an additional plate spring between two projected portions formed on the conventional base plate with a fixed interval, in order to reflect the laser beams into a direction of an optical sensor, that is, into a horizontal direction. Accordingly, the present invention can reduce the fabrication cost of a component.